The invention relates to a process for sealing soil formations in which a mineral sealing layer of a cohesive soil is applied, with addition of pulverulent waterglass, and is compacted mechanically.
Such a process using mineral sealing layers of naturally occurring soils is known from DE-C-27 02 787. By using pulverulent waterglass, the permeability coefficients k.sub.f of the mineral sealing layer can be improved to values in the range from 3.6 to 1.3.times.10.sup.-10 m/s.
A process for sealing soil formations in which sewage sludge or sludge from waters is mixed with 30 to 70% by weight, based on the sludge dry weight, of additive of stable grain which is capable of absorbing water and the resulting synthetic soil mixture is applied to the soil formation and compacted mechanically is furthermore known from EP-B 338 039. In a particular embodiment, it is intended here to carry out the process with the addition of sodium aluminate as an agent which forms a soft gel and pulverulent waterglass, the waterglass initially being mixed into the mixture in the dry form and the agent which forms a soft gel being mixed in by a further processing operation only after the waterglass has dissolved. Permeability coefficients k.sub.f of 5.times.10.sup.-10 to 3.times.10.sup.-11 m/s are stated for this synthetic soil system.
However, the process described in EP-B 338 039 has certain limitations, in particular because there are environmental objections because of the high content of harmful substances in the sewage sludge and its additives (such as power station ashes or refuse incineration ashes). Thus, for example, the use of such sewage sludge mixtures is not approved for base seals but only for top seals of dumps because of the high content of harmful substances. Apart from these limitations for certain synthetic soils, on the other hand, natural soils, such as clay-containing soils, which are most suitable for such seals and are approved per se for base seals, do not have an adequate harmful substances retention capacity in the long term and additionally undergo physicochemical change, which leads to an increase in permeability in the long term. This is also the reason for the development of the combi-seal in which a sealing web of plastic is provided over the clay sealing layer.